1. Field of the Invention
The present invention relates in general to a piezoelectric/electrostrictive actuator, and more particularly to such a piezoelectric/electrostrictive actuator which has a novel structure that assures improved and stable operating characteristics, and which can be produced with significantly improved efficiency.
2. Discussion of Related Art
In recent years, there has been known an actuator having a base member defining a pressure chamber, and a piezoelectric/electrostrictive element disposed on a wall of the pressure chamber, for raising the pressure of a fluid in the chamber so as to change the volume of the chamber. Such a piezoelectric/electrostrictive actuator may be used as an ink pump for a print head used in an ink jet printer, for example. To effect printing by the print head, an ink material is supplied to the pressure chamber to fill the same, and the pressure within the chamber is raised by displacement of the piezoelectric/electrostrictive element, so that ink particles are jetted through a nozzle which communicates with the pressure chamber.
Referring to FIGS. 5 and 6, there is illustrated an example of ink jet print head which uses as an ink pump the above-described piezoelectric/electrostrictive actuator. This print head has an ink nozzle member 16 which consists of a metallic nozzle plate 4 having a plurality of nozzles 2, a metallic orifice plate 8 having a plurality of orifices 6, and a channel plate 10, which are superposed on each other such that the channel plate 10 is interposed between the plates 4, 8. These plates 4, 8, 10 are bonded together into the ink nozzle member 16, so as to form a plurality of ink discharge channels 12 for leading or guiding an ink material to the respective nozzles 2, and at least one ink supply channel 14 for leading or supplying the ink material to the orifices 6. A piezoelectric/electrostrictive actuator 25 used as an ink pump for the print head includes a base member 24 consisting of two plates 18, 20 made of metal or synthetic resin and formed in lamination on the ink nozzle member 16. The base member 24 is formed with a plurality of voids 22 which correspond to the nozzles 2 and orifices 6. A plurality of piezoelectric/electrostrictive elements 28 corresponding to the respective voids 22 are secured to an outer surface of the plate 18 of the base member 24 of the actuator 25. With this actuator 25 superposed on and bonded to the ink nozzle member 16, each of the voids 22 provides an ink chamber 26 in which the pressure of the ink is raised by displacement of the corresponding piezoelectric/electrostrictive element 28.
In producing the actuator 25 used in the above print head, however, small pieces of the piezoelectric/electrostrictive elements 28 must be bonded to the walls of the respective ink chambers 26, which makes it extremely difficult to render the resulting print head sufficiently small-sized. Further, the bonding of the piezoelectric/electrostrictive elements 28 inevitably pushes up the cost of manufacture of the print head, and makes it difficult for the elements 28 to maintain sufficiently high reliability.
Further, it is extremely difficult to bond the actuator 25 to the ink nozzle member 16, since the spacing between the adjacent voids 22, 22 formed in the print head, that is, the thickness "t" of a partition wall 30 which separates the adjacent voids from each other, is considerably small, more precisely, about 1 mm or smaller.
More specifically, an adhesive used for bonding the ink nozzle member 16 and the actuator 25 is likely to overflow onto the opposite surfaces of the partition wall 30. Therefore, the ink chambers 26 and/or ink flow channels including the ink supply and discharge channels 12, 14 and orifices 6 may be deformed, whereby the ink-jetting characteristics of the print head may deteriorate, resulting in reduced quality and yield of the products (print heads).
If the amount of the adhesive applied is reduced to avoid its overflow as described above, it is likely that the ink nozzle member 16 and actuator 25 are insufficiently or poorly bonded together at some portions of the interface of the members 16, 24. This may result in incomplete sealing between the adjacent ink chambers 26, 26, causing leakage of the pressures of the ink chambers 26, 26 and consequent crosstalk, for example. The partial or insufficient bonding may also leave gaps between the bonding surfaces of the members 16, 24, resulting in pressure loss upon pressurizing of the ink chambers 26 due to the air remaining in the gaps. Consequently, the ink-jetting characteristics of the print head may be lowered.